Field of the Invention
The invention relates to a method for detecting a rotation direction in three-phase networks, in which the individual phases are respectively sampled at predetermined times. The European patent document EP 0 599 648 A1 describes such a method.
An electronic rotating field indicator is described on page 602 of the reference etz-b, 29 (1977). A pulse sequence is formed in order to determine the rotation direction, and the pulse sequence is used to derive conclusions relating to xe2x80x9ccounterclockwise rotationxe2x80x9d or xe2x80x9cclockwise rotationxe2x80x9d of the rotating field. Furthermore, a so-called antiphase detector is known from the Japanese patent document JP 55-13868 A2. The antiphase detector carries out a half-wave rectification.
Further, a phase detector is known from the Japanese patent document JP 55-114963 A2. The phase detector requires that all the phases must be sampled simultaneously at a number of points in time.
The German patent document DE 195 25 761 A1 describes a synchronization detection circuit having a pattern comparator. In addition, the European Patent Document EP 0 440 782 B1 describes a release or trigger system for interrupting at least a number of current paths in a polyphase network, which has a microcomputer.
The above-mentioned European patent document EP 0 599 648 A1 describes a three-phase line analyzer, which stores digital values of the signals in the three phases and, starting from a zero point, determines the positive signal series, negative signal series, and further signal series. The U.S. Pat. No. 4,278,937 A describes a circuit configuration which determines the phase sequence of a rotating field by comparing voltages of individual half waves. The German patent document DE 195 08 769 C1 describes a method for determining the direction of rotation of a three-phase system and a circuit configuration for performing the method, which determines the zero crossing of a phase while simultaneously determining the polarity of the other two phases. Using a microprocessor, the direction of rotation can be determined from a comparison of the polarities in relation to a zero point, however, determining the zero point crossing is comparatively complicated.
It is accordingly an object of the invention to provide a method for identifying the rotation direction in three-phase networks which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which is simple and can be automated. It is a further object of the invention to specify an advantageous use of such a method.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for identifying a rotation direction of a three-phase network, the method includes the steps of sampling individual phases of the three-phase network by alternately sampling the individual phases at given time intervals for generating measured values of the individual phases; evaluating the measured values of the individual phases with a given evaluation algorithm, the given evaluation algorithm defining a result quantity determined from the measured values of the individual phases sampled at least at two points in time; and determining a mathematical sign of the result quantity, the mathematical sign being significant for a rotation direction of the three-phase network. in accordance with another mode of the invention, the individual phases have an ideal sinusoidal profile and the mathematical sign is determined by evaluating the measured values of the individual phases during a single evaluation cycle.
In accordance with yet another mode of the invention, at least one of the individual phases has harmonics or an interference and the mathematical sign is determined by evaluating the measured values of the individual phases during a plurality of evaluation cycles.
In accordance with another mode of the invention, the individual phases of the three-phase network are sampled by alternately sampling the individual phases at a frequency of approximately nine times a network frequency.
Until now, the rotation direction of three-phase networks has often been detected using empirical methods. In practice, particularly for motor control circuits, it is necessary to equip already existing overload relays with additional functions for an operational monitoring or supervision. Such an additional function may advantageously be a rotation direction detection when the overload relay is used in three-phase networks, in order to avoid fault situations, for example when installation and modification work is carried out. Therefore, in accordance with an added mode of the invention, a digital overload relay performs the steps of sampling the individual phases of the three-phase network, evaluating the measured values of the individual phases, and determining the mathematical sign of the result quantity for detecting the rotation direction of the three-phase network.
In accordance with an added mode of the invention, the digital overload relay has a signal detection capability and/or a signal processing capability which are used for performing the steps of sampling the individual phases of the three-phase network, evaluating the measured values of the individual phases, and determining the mathematical sign of the result quantity.
With the objects of the invention in view there is also provided, a method for identifying a rotation direction of a three-phase network, which includes the steps of sampling individual phases of a three-phase network at given time intervals for generating measured values of the individual phases; evaluating the measured values of the individual phases with a given evaluation algorithm, the given evaluation algorithm describing a pattern of mathematical signs of the measured values sampled at least at two points in time; and deriving an unambiguous statement about one of a counterclockwise rotation and a clockwise rotation from a totality of mathematical sign changes of the measured values.
In accordance with another mode of the invention, the individual phases of the three-phase network are alternately sampled for generating the measured values.
In accordance with yet another mode of the invention, the individual phases are sampled at a given frequency, the given frequency differing by less than 30%, and preferably less than 15%, from three times a network frequency.
In accordance with a further mode of the invention, a digital overload relay is used to perform the steps of sampling the individual phases, evaluating the measured values, and deriving the rotation direction.
The object of the invention is achieved, according to the invention, in a first alternative, in that the individual phases are sampled alternately at predetermined time intervals, and in that a predetermined evaluation algorithm is used to evaluate the individual phases. The evaluation algorithm defines a result value or result quantity which is determined from measurement values of the individual phases sampled at least at two points in time. The mathematical sign of the result value is significant for xe2x80x9ccounterclockwise rotationxe2x80x9d or xe2x80x9cclockwise rotationxe2x80x9d of the three-phase current.
In a second alternative, the individual phases are sampled at given time intervals and are evaluated by a predetermined evaluation algorithm, such that the evaluation algorithm describes a pattern of the mathematical sign of the measurement values, which are determined by sampling at least at two points in time. A clear statement regarding xe2x80x9ccounterclockwise rotationxe2x80x9d or xe2x80x9cclockwise rotationxe2x80x9d can be derived from the totality of the mathematical sign changes of the measurement values.
An advantageous feature of the invention is that the individual phases are sampled alternately, or all three phases are sampled within a short measurement time interval, at predetermined time intervals. The measurement time interval may be, for example, 100 xcexcs. Particularly in a three-phase network, the sampling frequency may be approximately three times the network frequency.
According to the invention, a single evaluation cycle may be sufficient, particularly if there is an ideal sinusoidal profile. Such an evaluation cycle includes at least three measurement times.
According to a preferred embodiment of the first alternative of the invention, rectified signal profiles of the individual phases are evaluated. In this case, the individual phases may be half-wave (single-way) or full-wave (double-way) rectified.
In a preferred use, the method according to the invention is used specifically for a rotation direction detection using a digital overload relay. In this case, it is particularly advantageous that a digital signal controller and/or signal processing capability which already exists in the relay can be used to monitor the rotation direction.
For the latter use of the invention, it is now possible to determine the rotation direction in 50 Hz and/or 60 Hz networks in particular from half-wave-rectified three-phase current signals. This is particularly important since the analog portion of the signal detection which normally exists in overload relays can process only positive signals.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for detecting the rotation direction of three-phase networks, the use of this method, and an associated digital overload relay, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.